Sheet-straightening mechanism

ABSTRACT

An apparatus for straightening sheets of material carried by a conveyor includes a sheet-sensing switch on each side of the conveyor actuated by the leading edge of the sheet to indicate the magnitude and direction of misalignment. A timing circuit computes the time difference between the passage of the leading edge of each side of the sheet and controls the speed of drive motors which thereafter move the sides of the sheet independently of the conveyor to straighten it.

United States Patent [56] References Cited UNITED STATES PATENTSlnventors Carl W. Maxey;

Kenneth M. Cage, both of Everett, Wash.

O0 Mme 77 22% 8 9 m ."S m WT MI E n M mm m M W P u MN mwmm are S O 658 96 899 111 //l 2 6 207 2 7 509 568 5 3 3 m P m o C m w 9 mm 61 ww k t n7J Mo 27 m 9,. B m a ew 3M&TH 0. de N mm n8 d P ei Pumas AFPA 11]] 12532247 1,028,495 4/1958 Germany.............. l98/33(R2) Primary Examiner-Edward A. Sroka AnorneyMarechal, Biebel, French & Bugg [s 1 HE R GHTENING MECHANISM ABSTRACT: An apparatus for straightening sheets of materialcarried by a conveyor includes a sheet-sensing switch on each side ofthe conveyor actuated by the leading edge of the sheet to indicate themagnitude and direction of misalignment.

4 Claims, 3 Drawing Figs.

A timing circuit computes the time difference between the passage of theleading edge of each side of the sheet and controls the speed of drivemotors which thereafter move the sides of the sheet independently of theconveyor to straighten it.

PATENTEU SEP 7 IS?! SHEET 1 [IF 2 CONTROL CIRCUW 23 Ls-m. ML 22uvyavraes CARL W. MAXEY a. KENNETH M. CAGE ATTORNEYSSI-IEET-STRAIGHTENING MECHANISM BACKGROUND OF THE INVENTION Sheetmaterial, such as veneer sheets, carried on a conveyor system may becomemisaligned or twisted due to drag, differential belt speed, orimproperly placing the sheets initially on the conveyor. When thesesheets are moved by the conveyor to an automatic cutting machine, forexample, this misalignment could cause problems in cutting the sheets orin feeding them into the cutting machine.

SUMMARY OF THE INVENTION This invention relates to a method forstraightening sheet material and apparatus positioned intermediately ona conveyor for moving each sheet independently of the conveyor in such away that they are straightened as they pass therethrough. As the sheetsmove on a conveyor past the apparatus of this invention, they areintercepted by a pair of sheet-moving means, one placed on either sideof the conveyor. The sheet-moving means includes electric motors whichare operated normally at a speed which causes the sheet to move at thesame velocity as the conveyor. Sheet-sensing switches are placed oneither side of the conveyor immediately upstream of the sheet-movingmeans. These switches are actuated upon the arrival of the leading edgeof the sheet, and are connected to a timing circuit which measures thetime interval between actuation. This time interval therefore indicatesthe magnitude and direction of sheet misalignment. In the preferredembodiment, the lower speed of the motor in each sheet-moving meansmoves the sheets at the same speed as the conveyor. The timing circuitwill cause that motor on the side of the sheet which is trailing toincrease its speed for a time period related to the interval between theswitch closures, thus moving the sides of the sheet differentially andthereby straightening it on the conveyor.

It is an object of this invention to provide a method and apparatus forproperly orienting sheet material, such as veneer, on a conveyor system;to provide a sheet straighteningmethod and apparatus which employstwo-speed motors with driving means to engage the sheet after it passessensing means, such as switches, indicating the passage of the leadingedge of the sheet to determine the direction and magnitude of the sheetmisalignment, the driving means normally moving the sheet at the samevelocity as the conveyor upon which the sheet is carried until sheetmisalignment is detected, and then to move the sides of the sheetindependently of the conveyor, with the differential speed between thedriving means being a function of the time difference in the actuationof the sensing switches by the leading edge of the sheet.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a pictorial view showing asheet carried by a belt conveyor and showing the means for straighteningthe sheet including two-speed motors positioned at the sides of theconveyor and sheet actuated switches for sensing the magnitude anddirection of the misalignment of the leading edge of each sheet;

FIG. 2 is a plan view showing, in dotted lines, a misalignment sheetcarried by the conveyor, and showing the sheet in full lines after ithas been straightened by the two-speed motors; and

FIG. 3 is an electrical schematic drawing showing the timing means andcontrol circuit for supplying current to the twospeed sheet movingmotors located intermediately on the conveyor.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. ll, sheet material 10,such as veneer, is carried by a conveyor I2. in the examples shown, theconveyor includes a plurality of belts 13 which move the sheet It) tothe left at a constant speed. Other means may be employed to move thesheet, the conveyor shown being only one example of the type ofconveyors with which this invention can be used.

The sheet 10 is shown in FIG. 1 as being misaligned on the conveyorbelts 13. As the sheet moves down the conveyor 12, the left side of theleading edge M of the sheet will engage the sheet-sensing switch LS-Lbetween the right side of the leading edge of the sheet engagessheet-sensing switch LS-R. These sensing switches are electricallyconnected to a control circuit 15 which controls sheet-moving meansincluding a pair of two-speed motors ML and MR. These motors turn sheetdrive means which, in the preferred embodiment, are wheels 20 and 21,through belts 22. When the motors are turning at their lower speed, thewheels 20 and 21 move the sheet 10 at the same velocity as the belts 13.Pressure wheels 23 and 24 insure that the sheet is moved under thecontrol of wheels 20 and 21 independently of the conveyor belts 13.

Since there is a misalignment of the sheet 10 with respect to theconveyor 12, as shown in FIGS. l and 2, the control circuit will causethe motor MR to speed up for that period of time which is necessary tocause straightening of the sheet, and after the sheet is straightened,as shown by full lines in FIG. 2, the motor will return to its lowerspeed mode and the now straightened sheet will continue to be moved bythe motors at the same speed as the conveyor belt until it leaves thecontrol of the straightening wheels 20 and 21..

Other forms of sheet drive means may be employed, and in the case ofsheets having a narrow depth in the direction of travel, it will beadvantageous to use belts to move the sheets in place of the wheels 20and 211 so that these is a longer time period during which the sheets 10are under control of the sheet moving means.

Referring now to the electrical schematic diagram in FIG. 3, whichillustrates the control circuit and timing means of this invention, 1 10volt AC power is supplied to a transformer T1 through an on'off switchS1. This voltage is also applied to the primary winding of transformerT2. The secondary winding of transformer T1. is connected to a full wavebridge rectifier BR, the output of which is applied to one terminal ofeach of relays RY-I, RY-2, RY-3 and RY-4 from a common connectionlabeled A in FIG. 3. The output of this rectifier is also suppliedthrough a filter network including capacitor C1 and resistors RI and R2to contacts 30 and 31 of relays RY-l and RY-3, respectively.

In the example shown in FIGS. 1 and 2, the leading edge of the sheet atthe left side first engages the left sheet sensing switch LS-L. Thisswitch is a double-pole, double-throw LS-L, and is shown in FIG. 3, asbeing in the; normal or nonactuated position. Upon RY-Z of the switchLS-L, the upper contact 33 causes a ground to be placed through thenormally closed contacts 32 of relay RY-3 to energize relay RY-ll. Atthis time, the now closed contacts 31 of relay RY-l close to supplycurrent from the rectifier HR through the normally closed contacts 34 ofrelay RY-2 to the timing capacitor CL. The charging rate of thiscapacitor is determined by the setting rheostat R3. Previous to theclosure of switch LS-L, timing capacitor CL was grounded through thenormally closed con tacts 35 of the switch LS-L.

Upon closure of sheet-sensing switch LS-R, indicating that the leadingedge of the sheet at the right side of the conveyor is now passing thesheet-sensing switch position or reference location, a ground will beplaced through contacts 36 of LS-R and through the normally opencontacts 37 of relay RY-l to energize relay RY-2. This discharge pathincludes resistor Rd and potentiometer R5, and the discharge rate may beadjusted by the setting of the adjustable tap on potentiometer R5. Atthe same time, a gating voltage is applied to the gate electrode ofsilicon-controlled rectifier SCR-L through resistor R6 causing thatsemiconductor device to go into the conducting state, and relay RY 6will energize as a result since current from transformer T2 is nowapplied to its coil through contacts 38 of relay RY-2.

As shown at the extreme right in FIG. 3, motors MR and ML each includetwo windings, the first winding causing the motor to turn at 900 rpm,and the second winding causing the motor to turn at 1200 r.p.m. Duringnormal operation, the motors are turning at 900 rpm. since power issupplied to the motor through the normally closed contacts 39 and 40 ofrelays RY-S and RY-6. With RY-6 now energized, the 1200 rpm. winding isenergized, and therefore the right-hand motor MR will speed up for theperiod of time that SCR-L is gated on. As the capacitor CL discharges,the gate voltage on SCR-L will eventually be reduced below its firingvoltage, and at that time, relay RY-6 will deenergize and return themotor to its normal operating speed.

Relays RY-S and RY-6 are AC relays which receive their current from theisolating transformer T2. Alternating current is used in this embodimentof the invention to allow the silicon-controlled rectifiers SCR-L andSCR-R (GE type C22B) to return to the nonconducting state as soon as thevoltage on the gate electrode falls below a predetermined level. Thisprovides accurate and repeatable control over the time interval duringwhich these rectifiers conduct. Thus the amount of charge on capacitorCL is determined by the difference in time between the closure of switchLS-L and switch LS-R and the setting or value of potentiometer R3, whilethe discharge rate of the capacitor is determined by resistance valuesof R3, R4 and R5.

After passage of the sheet 10, the sheet-sensing switches LS-L and LS-Rreturn to their normal positions, as shown in FIG. 3, thus placing aground on capacitor CL through contacts 35 of switch LS-L and oncapacitor CR through contacts 42 of switch LS-R so that these capacitorswill always begin charging from a zero voltage level to insure accurateand repeatable timing characteristics from the control circuit.

If the sheet were misaligned in a direction opposite from that shown inFIGS. 1 and 2, it is apparent that the portion of the circuit shown atthe top of FIG. 3 would be effective to cause the left-hand motor ML toincrease speed for a time sufficient to straighten the sheet on theconveyor. Thus upon the closure of switch LS-R, relay RY-3 willenergize, and capacitor CR will begin charging through contacts 43 ofrelay RY-4 and the now-closed contacts 30 of relay RY-3. The chargingrate of capacitor CR is determined by the setting of potentiometer R7.Upon closure of switch LS-L, relay RY-4 will energize and capacitor CRwill discharge through resistor R8 and potentiometer R9, and whiledischarging, a gating voltage will be applied to the gate electrode ofthe silicon-controlled rectifier SCR-R through resistor R10. Since relayRY-4 is now energized, voltage from the secondary transformer T2 will beapplied through RY-4 contacts 44 to relay RY-S which energizes to supplycurrent to the higher speed windings of motor ML. The silicon-controlledrectifier SCR-R will return to the nonconducting state when its gatevoltage falls below a predetermined value as capacitor CR discharges,and deenergization of relay RY-5 will cause the motor to return to itsnormal operating speed. After the trailing edge of the sheet passes thesheet-sensing switches, they will return to their normal position asshown in FIG. 3.

Thus capacitors CR and CL develop timing signals which represent thedifference in time between the passage of the I leading edge of eachside of the sheet in response to actuation of sheet-sensing switchesLS-L and LS-R and then control the time the motor on that side of theconveyor where the leading edge trails operates at its higher speed sothat each misaligned sheet is straightened on the conveyor.

Obviously, the speed of motors ML and MR may be decreased rather thanincreased to effect sheet straightening while utilizing the same orsimilar circuit as that shown in FIG. 3. For example, relay RY-S couldbe connected to the windings of the motor which controls the speed ofthe right edge of the sheet, and in the deenergized state apply currentto the higher speed winding which causes the sheet to move at the samevelocity as the conveyor. When relay RY-S is energized, it would supplycurrent to a lower speed winding to retard the movement of the rightside of the sheet relative to the conveyor and thus cause the sheet tobecome aligned with the conveyor.

The circuit thus described utilizes an RC timing circuit, and thedifferences in acceleration and deceleration of the motors, the relayand contactor lays, and mechanical element slippage factors, combine toprovide a practically perfectlypompensating system. If more precisecontrol is desired, the timing and control functions could be performedby using linear circuits while continuing to follow the teachings ofthis invention.

While the method and form of apparatus herein described constitutes apreferred embodiment of the invention, it is to be understood that theinvention is not limited to this precise method and form of apparatus,and that changes may be made therein without departing from the scope ofthe invention which is defined in the appended claims.

What is claimed is 1. Method of straightening individual sheets ofmaterial carried by conveyor means comprising the steps of establishingthe difference in time between passages of opposite ends of the leadingedge of each side of the sheet past a reference location intermediatelylocated on the conveyor means;

controlling the speed of each side of the sheet independently of theconveyor means; and

ditferentially moving the sides of each sheet in response to saiddifference in time by an amount and in a direction such that the sheetis aligned with said reference location on the conveyor means whereinthe side of the sheet which trails is accelerated momentarily to ahigher speed for a period of time related to the difference between thetime each side of said sheet passes said reference location.

2. Apparatus for straightening individual sheets of material carried bya conveyor comprising means on each side of the conveyor for detectingthe passage of the leading edge of the sheet; timing means responsive tosaid sensing means for developing a signal representing the differencein time between the passages of opposite ends of the leading edge ofeach side of the sheet relative to said detecting means; and

means mounted on each side of the conveyor for moving the adjacent sideof the sheet independently of the conveyor, said means being controlledby said timing signal so that, as the sheet passes through said movingmeans, the edges of the sheet may be moved differentially and the sheetstraightened relative to the conveyor. 3. Apparatus for straighteningindividual sheets of material carried by a conveyor comprising means oneach side of the conveyor for detecting the passage of the leading edgeof the sheet including switches mounted on each side of the conveyor,said switches being actuated by the leading edge of each sheet;

timing means responsive to said sensing means for developing a signalrepresenting the difference in time between the passage of opposite endsof the leading edge of each side of the sheet relative to said detectingmeans; and

means mounted on each side of the conveyor for moving the adjacent sideof the sheet independently of the conveyor;

said moving means being controlled by said timing signal so that, as thesheet passes through said moving means, the edges of the sheet may bemoved differentially and the sheet straightened relative to theconveyor;

said moving means including a two-speed motor having drive means mountedto engage each side of the sheet after it passes said switch means, saidmotor having a first speed which moves the sheet at the same velocity asthe conveyor, and a second speed which will accelerate the sheet to ahigher velocity relative to the conveyor;

said timing signal being operative to energize said motor on that sideof the conveyor where the leading edge of the sheet trails so that saidmotor operates at the higher speed for a time period which is determinedby the difference in time between the actuation of each of said switchmeans.

4. Apparatus as defined in claim 3 wherein said timing means includesmeans sensing the magnitude of the charge on said capacitor to energizesaid motor on that end of the sheet which trails at the higher speed fora time period which is determined by the quantity of the charge on saidcapacitor.

*ggggg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,603,446 Dated September 7, 1971 Inventor(s) Carl Maxey and Kennethcage It is certified that error appears in the above-identified patentand that said Letters Patent are hereby corrected as shown below:

{- Column 2 line 6 "between" should read before Column 2, line 30,"these" should read there Column 2, line 48, "LS-L should read switchColumn 2, line 49, "RY-2" should read closure Column 4, line 34,"detecting" should read sensing Column 5, line 6, "heading" should readleading Signed and sealed this 13th du r of April 1 972.

( S .JAL

Attost:

EDZJAHD I"I.l'U. TCIlLL1h, Jli. ROBERT GOTTSCHMJK Attesting OfficerCommlssionor of Patents

1. Method of straightening individual sheets of material carried byconveyor means comprising the steps of establishing the difference intime between passages of opposite ends of the leading edge of each sideof the sheet past a reference location intermediately located on theconveyor means; controlling the speed of each side of the sheetindependently of the conveyor means; and differentially moving the sidesof each sheet in response to said difference in time by an amount and ina direction such that the sheet is aligned with said reference locationon the conveyor means wherein the side of the sheet which trails isaccelerated momentarily to a higher speed for a period of time relatedto the difference between the time each side of said sheet passes saidreference location.
 2. Apparatus for straightening individual sheets ofmaterial carried by a conveyor comprising means on each side of theconveyor for detecting the passage of the leading edge of the sheet;timing means responsive to said sensing means for developing a signalrepresenting the difference in time between the passages of oppositeends of the leading edge of each side of the sheet relative to saiddetecting means; and means mounted on each side of the conveyor formoving the adjacent side of the sheet independently of the conveyor,said means being controlled by said timing signal so that, as the sheetpasses through said moving means, the edges of the sheet may be moveddifferentially and the sheet straightened relative to the conveyor. 3.Apparatus for straightening individual sheets of material carried by aconveyor comprising means on each side of the conveyor for detecting thepassage of the leading edge of the sheet including switches mounted oneach side of the conveyor, said switches being actuated by the leadingedge of each sheet; timing means responsive to said sensing means fordeveloping a signal representing the difference in time between thepassage of opposite ends of the leading edge of each side of the sheetrelative to said detecting means; and means mounted on each side of theconveyor for moving the adjacent side of the sheet independently of theconveyor; said moving means being controlled by said timing signal sothat, as the sheet passes through said moving means, the edges of thesheet may be moved differentially and the sheet straightened relative tothe conveyor; said moving means including a two-speed motor having drivemeans mounted to engage each side of the sheet after it passes saidswitch means, said motor having a first speed which moves the sheet atthe same velocity as the conveyor, and a second speed which willaccelerate the sheet to a higher velocity relative to the conveyor; saidtiming signal being operative to energize said motor on that side of theconveyor where the leading edge of the sheet trails so that said motoroperates at the higher speed for a time period which is determined bythe difference in time between the actuation of each of said switchmeans.
 4. Apparatus as defined in claim 3 wherein said timing meansincludes a capacitor which begins charging upon the closure of thatswitch sensing the end of the leading edge of the sheet which firstarrives at said detecting means, and which ceases charging and beginsdischarging at a predetermined rate upon the closure of that switchsensing the end of the heading edge of the sheet which trails; and meanssensing the magnitude of the charge on said capacitor to energize saidmotor on that end of the sheet which trails at the higher speed for atime period which is determined by the quantity of the charge on saidcapacitor.